V8 started to depend on LLVM's libm

[joyeecheung]

https://github.com/nodejs/node-v8/actions/runs/25719364307/job/75516558363

v8/out/Release/obj.target/v8_libbase/deps/v8/src/base/numbers/bignum-dtoa.o
../deps/v8/src/base/ieee754.cc:36:10: fatal error: 'third_party/llvm-libc/src/shared/math.h' file not found
   36 | #include "third_party/llvm-libc/src/shared/math.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Broken since May 9. Caused by https://chromium-review.googlesource.com/c/v8/v8/+/7828379 which started using LLVM's libm in V8

[joyeecheung]

@MayaLekova is going to take a look

[targos]

I mentioned this on the v8-canary Slack channel. I have made some fixes that work locally.

[targos]

Gyp change: nodejs/node@bd4661e
node-core-utils PR: nodejs/node-core-utils#1073

[MayaLekova]

Thanks for including me!

I reproduced the missing header error locally and tried applying a change in deps/v8/third_party/llvm-libc/BUILD.gn similar to

group("headers") {
  visibility = [ "//v8:v8_libbase" ]
  public_configs = [ ":config" ]
}

as per advice in this CL: https://chromium-review.googlesource.com/c/v8/v8/+/7828379.

This alone didn't fix the issue (no math.h generated in deps/v8/third_party/llvm-libc/), but I think something along those lines should be the way to go. For instance deps/v8/third_party/jsoncpp/generated/version.h is maybe generated in a similar manner, but I need to look at it further (and my understanding of GN is outdated, to put it mildly).

[joyeecheung]

Note that in Node.js we don't use gn, the builds are done through gyp.